Heat exchangers developed up to the present time may generally be classified into two categories, namely tubular exchangers and plate exchangers. The conventional plate heat exchangers are manufactured by stacking a plurality of plates, configured in a way so that two fluids, one relatively hot and the other relatively cold, may be passed between alternating channels formed by the plates. Plate heat exchangers may be further broken down into two categories, namely gasket-containing heat exchangers and all-welded heat exchangers. Gasketed exchangers have many advantages over all welded exchangers, three of which being the accessibility of plates for cleaning, lower thermal stresses, and cost per area; however, distinct limitations are present. Gasket limitations occur with temperature, pressure, and compatibility with fluids used. To overcome these limitations, plate heat exchanger manufacturers have developed all welded plate heat exchangers. The major problem encountered with existing all welded units is the excessive thermal stresses present which leads to shorter equipment life. High manufacturing cost of separating the relatively hot and relatively cold fluid via common welding procedures and excessively thick heat transfer plates are other disadvantages.
U.S. Pat. No. 5,469,914, issued on Nov. 28, 1995, Roger C. Davidson and Achint P. Mathur discloses an all welded plate heat exchanger essentially formed by stacking elongated heat transfer plates having solid metal fillers along the two elongated sides, continuous TIG welding the fillers to the plates, and welding inlet and outlet headers for two or more fluids. The continuous welding of the two elongated sides results in higher manufacturing cost and difficulties in allowing for the differential thermal expansion of the plates. In addition, this method eliminates the possibility of repairing common weld failures.
U.S. Pat. No. 4,688,631, issued on Aug. 25, 1987, Andre Peze and Henry Fechner discloses a similar all welded plate heat exchanger essentially formed by welding pairs of plates containing multiple depressions thereby forming cassettes, via an electric seam welding method. The cassettes are then stacked while the extending flanges of the cassettes are bent ninety degrees and welded together, via an arc welding method, to seal off the secondary channels. The depressions are then spot welded to the adjacent plate for additional support. Inlet and outlet headers are then attached for two or more fluids. This solution improves the capacity of the exchanger to accommodate differential expansion; however, only slightly and at the expense of pressure containment. The need for relatively thick metal plates still appears to exist if substantial pressure ratings are to be obtained. In addition, repairs on the seam-welded cassettes do not appear feasible via this solution due to the continuous welding along the flange of the plates.
Neither of the above described heat exchangers, either individually or in combination, is seen to describe the present invention as claimed.
The objective of the present invention is to construct a plate heat exchanger, which more efficiently accommodates manufacturing cost, thermal expansion, and pressure containment than prior developed plate heat exchangers. This objective is achieved according to the present invention by replacing the continuous sealing of the two sides of a pair of adjoining rectangular cassettes, in which electric seam welding has been performed, with baffle clips and enclosing such clips in headers extending the length of the cassettes. The presence of the full length headers allows the baffle clips to be applied without welding or with only partial welding because the baffle clips are only acting in the capacity to prevent cross-flow and not fluid containment. This method of construction allows the internal pressure of the secondary fluid to be contained via the full length headers which when provided with an arcuate cross-sectional shape can contain moderately high pressures with relatively thin material. The baffle clips may be altered or removed to better facilitate the collection and distribution of fluids during condensation and or evaporation processes.